The headlines say youth is being served on the U.S. Olympic track and field team.

The numbers say that's nothing new.

With the second half of Olympic track trials set to start Thursday, 35 of the 50 athletes who have already guaranteed themselves trips to Rio de Janeiro will be going to their first Olympics. That sort of turnover is pretty much the norm. Data supplied by USA Track and Field shows an average of 53 percent turnover from year to year on the most recent world championship and Olympic teams, which essentially award the same number of spots through the same qualifying process. When the gap is two years, the turnover rate is 60 percent.

This year's group of newcomers includes 18-year-old high jumper Vashti Cunningham, the world indoor champion, who will be the youngest U.S. track and field athlete to qualify for the Olympics since Carol Lewis in 1980. The team also includes high jumper Chaunte Lowe and sprinter Allyson Felix, both of whom are in their 30s and going for the fourth time.

"You look at the system we have and the depth of talent we have, and one thing that's fairly consistent is that we'll have an amazing team and amazing athletes," USATF CEO Max Siegel said. "It's just a matter of who the stars are going to be. It's also the challenge of how we select them."

The U.S. won 29 medals at the London Olympics four years ago. That number dwindled to 18 at last year's world championships, raising alarm among some in track circles.

Over the years, the USATF has settled on a system in which the top three finishers in each event make it, assuming they have met an Olympic qualifying standard. There are no exceptions for injuries or past performances the way there are in many countries, including Jamaica, where Usain Bolt will almost certainly be on the team despite pulling out of Jamaica's qualifier with a hamstring injury.

It may be the fairest system, but, as decathlete Ashton Eaton said, "if the goal is to send the best team, I'm not sure the trials method is the best method."

For instance, a tangle of feet in the stretch of the women's 800-meter final knocked out Brenda Martinez and Alysia Montano, either of whom would've contended for medals. Making it instead were three first-timers: Kate Grace, Ajee Wilson and Chrishuna Williams.

"Surreal," said Grace, who was ranked seventh nationally coming into trials but had a gold medal around her neck Monday night. "I've never podiumed at a national event, and now I'm going to the Olympics. I knew I could run at this level even though I'd never done it before."

A few strange twists aside, most of these newcomers have been setting themselves up for success for years leading up to the Olympics. A look at some U.S. first-timers with the best chances of bringing home hardware from Rio:

SAM KENDRICKS: The 23-year-old pole vaulter actually flew to Eugene in 2012, expecting to compete at the Olympic trials then. By the time he landed, he learned that he'd been scratched from the field by a few late entrants who ranked higher than he did. He watched from the stands, and said that was the prime motivator to reach this point: He's currently ranked second in the world.

TORI BOWIE: The 25-year-old said her grandmother essentially "rescued" her as an infant by taking her in from a foster home. Bowie's favorite sport was basketball, but her grandmother pushed her into track, a move that has paid off. She won the 100-meter bronze medal at world championships last year and should contend in Rio. Also in the sprint mix: English Gardner.

JOE KOVACS: The 27-year-old is the defending world champion in shot put. He finished fourth at Olympic trials in 2012. Growing up, Kovacs was a football player who just used track and field to stay in shape. But then he started taking it more seriously. Kovacs' shot put coach as a kid: his mother, Joanna.

TRAYVON BROMELL: World-indoor champion at 60 meters and tied for bronze at 100 meters in Beijing. At 5-foot-9, will be looking up — way up — at the 6-foot-5 Bolt in the starting block. Bromell's U.S. teammate, Justin Gatlin, is considered the biggest threat to the Jamaican, but the 20-year-old from Baylor ran 9.84 seconds in the trials, second best in the world this year, on a sore Achilles.

EMILY INFELD: She may have only the 32nd-best time at 10,000 meters this year, but you can never count her out. She made headlines last year at world championships by running hard to the line to edge out teammate Molly Huddle for the bronze medal, after Huddle raised her hands to celebrate a step before the finish line.